1. Field of the Invention
The invention relates to testing devices, and more particularly to method and apparatus for testing the effects of irradiation on metal-oxide-semiconductor devices.
2. Prior Art
In the manufacture of metal-oxide-semiconductor (MOS) or metal-insulator-semiconductor (MIS) integrated circuits it is frequently desirable to determine whether the manufactured devices meet certain military specifications for radiation survivability, or hardness. Such hardness testing currently typically involves actual exposure to radiation at an irradiation facility and thus does not permit the devices to be tested on the manufacturing line.
Alternatives to this form of testing have been suggested, and include the use of an electron beam, generated by a scanning electron microscope, to irradiate the device under test and to observe the device response. This procedure, however, must be performed in a vacuum chamber, is slow and inconvenient, and requires an expensive electron microscope, all of which increases the expense involved in performing the desired test.
Still another alternative utilizes high field avalanche injection of holes into the silicon dioxide insulator from the silicon substrate to simulate radiation, as discussed in Aitken and Young, "Avalanche Injection of Holes in SiO.sub.2 ", IEEE Trans. Nucl. Sci., Volume NS-24, page 2128, December 1977. Use of this approach requires a heavily doped silicon substrate, which is not typically available on MOS integrated circuits. Further, since holes are injected under a negative bias and a heavily doped substrate is used, the measurement is relatively insensitive to hole trapping at the insulator-semiconductor interface and to interface state buildup, which are the most important parts of the radiation response.